1. Field of the Invention
The present invention relates to silicone surfactants for use in inert gas blown polyurethane foams. More particularly, the present invention relates to silicone surfactants having dimethyl siloxane backbones with attached polyalkylene oxide polyether pendant groups that preferably are designed to have flame-retardant characteristics for use in flame retardant (FR) foam compositions.
2. Description of Relited Art
Historically, numerous grades of polyurethane foams were blown with chlorofluorocarbon (CFC) based blowing agents to reduce foam density, control foam firmness, and cool the foams to minimize discoloration, degradation, and possible foam ignition problems. Worldwide issues regarding ozone depletion in connection with certain CFCs has led to the Montreal Protocol, which phases out the use of CFCs.
Thus, the polyurethane foam industry has tried to achieve the same foam grades and quality produced using alternate blowing agents (ABAs). Many different ABAs have been evaluated, including HCFC-141b, HFC-134a, HFC-22, alkyl carbonates, and pentane. In flexible slabstock foams, in particular, other approaches have been taken, including the use of acetone, methylene chloride, carbon tetrachloride, trichloroethane, and pentanes as ABAs. While functional, these approaches also have problems, including flammability, volatile organic compound (VOC) limitations, and toxicity (for the chlorocarbons).
More recently, technology has been developed that entails the use of supplemental added inert gases, e.g., CO2, as part of the blowing agent for flexible polyurethane foams, which is described in European Patent Publication No. 0 645 226 A2 (see also U.S. Pat. Nos. 5,620,710; 5,629,027; and 5,639,483; and U.S. Pat. Nos. Re. 37,012; 37,075; and 37115); U.S. Pat. No. 6,005,014; U.S. Pat. No. 6,147,133; and U.S. Pat. No. 6,326,413. This technology will hereinafter be referred to as xe2x80x9cDissolved Gas Technologyxe2x80x9d. Auxiliary gas is added to the system as a blowing agent and is used in conjunction with the CO2 generated from the reaction of isocyanate with water. More particularly, these patents disclose a process and a system for the continuous manufacture of polymeric foams. Reactive chemical components and additives comprising a low boiling blowing agent are mixed under pressure; the mixture is then frothed before chemical reaction takes place by feeding the mixture through a pressure equalizing and frothing device having a pressure-drop zone, of varying design, with eventual discharge of the froth onto a moving substrate.
U.S. Pat. Nos. 4,814,409 and 4,855,329 disclose certain polysiloxane-polyoxyalkylene compositions and their use as stabilizers in the manufacture of polyether polyurethane foam. These compositions have a polysiloxane chain substituted with at least two types of polyoxyalkylene polymers as pendants from the silicon atoms of the polysiloxane. The distinctive feature of these compositions is the specific selection of polyoxyalkylene polymers. Preferably, the polyoxyalkylene polymer pendants are provided as at least three different polyoxyalkylene polymers. One of these polyoxyalkylene polymers is composed of only oxypropylene units. This polyoxypropylene has an average molecular weight from about 130 to about 1200 excluding link and endcap. The other polyoxyalkylene polymers are composed of both oxyethylene and oxypropylene units. These references teach that silicone surfactants with lower ratios of unmodified polydimethylsiloxane groups to branched siloxane groups are preferred in flame retardant foam applications. This teaching is reinforced by Weier et al. in Proceedings of the Polyurethane 1994 Conference, 202 (1994).
U.S. Pat. No. 5,145,879 discloses silicone surfactants having a siloxane backbone and a mixture of high and low atomic mass oxyalkylene pendant groups, these polyether pendants having average atomic masses of 1500-6000 and 300-750 respectively. The surfactants operate in polyurethane foam compositions to provide stable foams over a range of surfactant concentrations while still producing product foams having relatively constant breathability. Also disclosed are polyurethane foam compositions which include the surfactants, a method of making polyurethane foam using the surfactants, and polyurethane foam made by the method.
U.S. Pat. No. 5,525,640 discloses that the use of inert gases as an auxiliary blowing agent in flexible polyurethane foams places unexpected requirements on the composition of the silicone surfactants used in such foams and typical silicone polyalkylene oxide polyether copolymer comb-type surfactants containing greater than about 37% ethylene oxide in the polyoxyalkylene-polysiloxane copolymer cause large cells when added inert gas is used as the blowing agent.
U.S. Pat. No. 5,789,454 discloses a method of using inert gas as an auxiliary blowing agent in the production of flexible polyurethane foams, in the presence of a blend of a silicone surfactant stabilizer and a second silicone compound. The disclosed method provides better stabilization of the foams made by such processes. Also disclosed are foam formulations containing such blends.
The disclosures of the foregoing are incorporated herein by reference in their entirety.
Previously, it was expected that all silicone surfactants currently used in the preparation of conventional slabstock foams would function well in stabilizing Dissolved Gas Technology foams. This would thus lead to fine cell structure foam prepared via all inert gas blowing. U.S. Pat. Nos. 5,525,640 and 5,789,454 taught that specific classes of surfactant structures are more applicable to Dissolved Gas Technology foaming.
It has now been discovered that other specific classes of silicone surfactants are efficient at yielding uniform low density Dissolved Gas Technology foams that exhibit good to excellent bulk foam stability and fine cell structure, particularly when lower use levels of surfactants are employed. Lower use levels of surfactants are economically desirable, but are known to exaggerate or stress any existing foam processing issues.
The present invention is directed to certain low to moderate molecular weight (hereinafter xe2x80x9cMWxe2x80x9d) surfactants that are comb-type FR silicone copolymers possessing no high ethylene oxide (xe2x80x9cEOxe2x80x9d) content branches that yield Dissolved Gas Technology foams having improved consistency as compared to other surfactant compositions.
More particularly, the present invention is directed to a method of producing a polyurethane foam comprising:
A) preparing a mixture comprising:
(1) a polyether polyol containing an average of more than two hydroxyl groups per molecule,
(2) an organic polyisocyanate,
(3) at least one catalyst for the production of polyurethane foams,
(4) water, and
(5) a surfactant;
xe2x80x83wherein the surfactant comprises a silicone/polyether composition of the formula:
Rxe2x80x94Si(CH3)2Oxe2x80x94{Si(CH3)2Oxe2x80x94}xxe2x80x94{SiCH3R1Oxe2x80x94}axe2x80x94{SiCH3R2Oxe2x80x94}bxe2x80x94{SiCH3R3Oxe2x80x94}cxe2x80x94{SiCH3R4Oxe2x80x94}dxe2x80x94Si(CH3)2xe2x80x94R;
xe2x80x83or the formula:
Rxe2x80x94Si(CH3)2Oxe2x80x94{SiCH3RO}mxe2x80x94(SiCH3{Oxe2x80x94(SCH3RO)mxe2x80x94Si(CH3)2R}O)nxe2x80x94{SiCH3RO}mxe2x80x94Si(CH3)2xe2x80x94R
xe2x80x83wherein:
R1, R2, and R3 are polyalkylene oxide polyethers of the formula
xe2x80x94Bxe2x80x94CnH2nOxe2x80x94(C2H4O)exe2x80x94(C3H6O)f(C4H8O)gZ,
xe2x80x83where
R1 has a blend average molecular weight in the range of from about 3000 to about 6000 grams/mole and ethylene oxide is from about 20 to about 60 weight percent of the alkylene oxide content of the polyether;
R2 has a blend average molecular weight in the range of from about 800 to about 2900 and ethylene oxide is from about 20 to about 60 weight percent of the alkylene oxide content of the polyether;
R3 has a blend average molecular weight in the range of from about 130 to about 800 grams/mole and ethylene oxide is from 0 to about 75 weight percent of the alkylene oxide content of the polyether;
R4 is an substituted or unsubstituted alkyl, alkaryl, or aryl group of C1 to C12;
B is derived from a moiety capable of undergoing hydrosilation;
Z is selected from the group consisting of hydrogen, C1-C8 alkyl or aralkyl moieties, xe2x80x94C(O)Z1, xe2x80x94C(O)OZ1, and xe2x80x94C(O)NHZ1,
where Z1 represents mono-functional C1-C8 alkyl or aryl moieties;
each R is independently selected from the group consisting of R1, R2, R3, and R4;
x is 40 to 150;
y is 5 to 40 and equals a+b+c+d,
where b or c, but not both, may be 0,
d/(a+b+c)=0 to 1, and
a+b greater than 0;
x/yxe2x89xa710;
m=10 to 100;
nxe2x89xa74; and
e, f, and g are defined by the molecular weight required by the polyether;
with the proviso that the total ethylene oxide content of the surfactant structure is less than 37% by weight; and
B) blowing the polyurethane foam with a pressurized inert gas.
As stated above, the present invention is directed to certain low to moderate MW surfactants that are comb-type silicone copolymers, preferably comb-type FR silicone copolymers, possessing no high EO content branches, which yield Dissolved Gas Technology foams having improved consistency as compared to other surfactant compositions.
The noted surfactant compositions showed the most differentiation when the foam was produced using relatively low levels of these stabilizing FR surfactants. Specifically, Dissolved Gas Technology foams prepared from such silicone compositions simultaneously possess good to excellent bulk foam stabilities and fine cell structures, even when lower levels of surfactant are employed.
Bulk foam stability is required during foam processing to ensure desired foam product consistencyxe2x80x94density, IFD (Indentation Force Deflection, a measurement of the degree of foam hardness/softness), density gradient, IFD gradients, airflow, and the like, over the cross section of the foam article produced. Foam of fine cell structure is strongly desired by foam customers, who view this property as a measure of foam quality and, hence, surfactant quality/suitability.
This finding of the excellent performance of the silicone copolymers of the present invention in foam produced by Dissolved Gas Technology was particularly unexpected, since silicone copolymers of higher EO content, including ones based on branches that are 100% by weight EO, function extremely well in most varieties of conventionally blown, i.e., no added inert gas, urethane foams. As such foam is commonly produced in the commercial flexible foam market, it was believed that these surfactant compositions would also do well in the all inert gas blown foam.
The silicone surfactants of the present invention have dimethyl siloxane backbones with attached polyalkylene oxide polyether pendant groups, i.e., xe2x80x9ccombxe2x80x9d copolymers. The Sixe2x80x94C bonds in these copolymers are hydrolytically stable, and many of these surfactants can be used in water amine premixes and are preferably designed with flame-retardant characteristics for use in flame retardant foam compositions.
The surfactants employed in the practice of this invention are silicone/polyether compositions having one of the following generalized average formulae:
Rxe2x80x94Si(CH3)2Oxe2x80x94{Si(CH3)2Oxe2x80x94}xxe2x80x94{SiCH3R1Oxe2x80x94}axe2x80x94{SiCH3R2Oxe2x80x94}bxe2x80x94{SiCH3R3Oxe2x80x94}cxe2x80x94{SiCH3R4Oxe2x80x94}dxe2x80x94Si(CH3)2xe2x80x94R;
or
Rxe2x80x94Si(CH3)2Oxe2x80x94{SiCH3RO}mxe2x80x94(SiCH3{Oxe2x80x94(SiCH3RO)mxe2x80x94Si(CH3)2R}O)nxe2x80x94{SiCH3RO}mxe2x80x94Si(CH3)2xe2x80x94R
wherein:
R1, R2, and R3 are polyalkylene oxide polyethers of the formula
xe2x80x94Bxe2x80x94CnH2nOxe2x80x94(C2H4O)exe2x80x94(C3H6O)fxe2x80x94(C4H8O)gxe2x80x94Z,
xe2x80x83where
R1 has a blend average molecular weight (xe2x80x9cBAMWxe2x80x9d, the numerical molar average molecular weight of a mixture of one or more distinctly different compositions) in the range of from about 3000 to about 6000 grams/mole and ethylene oxide comprises from about 20 to about 60 weight percent of the alkylene oxide content of the polyether;
R2 has a BAMW in the range of from about 800 to about 2900 and ethylene oxide comprises from about 20 to about 60 weight percent of the alkylene oxide content of the polyether;
R3 has a BAMW in the range of from about 130 to about 800 grams/mole and ethylene oxide comprises from 0 to about 75 weight percent of the alkylene oxide content of the polyether;
R4 is a C1 to C12 substituted or unsubstituted alkyl group, an alkaryl group, or an aryl group;
B is derived from a moiety capable of undergoing hydrosilation;
Z is selected from the group consisting of hydrogen, C1-C8 alkyl or aralkyl moieties, xe2x80x94C(O)Z1, xe2x80x94C(O)OZ1, and xe2x80x94C(O)NHZ1,
where Z1 represents mono-functional C1-C8 alkyl or aryl moieties;
each R is independently selected from the group consisting of R1, R2, R3, and R4;
x is 40 to 150;
y is 5 to 40 and equals a+b+c+d,
where b or c, but not both, may be 0,
d/(a+b+c)=0 to 1, and
a+b greater than 0;
x/yxe2x89xa610;
m=10 to 100;
nxe2x89xa64; and
e, f, and g are defined by the molecular weight required by the polyether; with the proviso that the total ethylene oxide content of the surfactant structure is less than 37% by weight.
The R1 moieties are preferably in the range of from about 35 to about 55% by weight of EO and, more preferably, about 40% EO. It is preferred that such moieties have a BAMW greater than 3500 daltons and, more preferably, greater than 4000 daltons. The R2 moieties are also preferably in the range of from about 35 to about 55% by weight of EO and, more preferably, about 40% EO. Preferably, such moieties have a BAMW in the range of from about 1100 to about 2300 daltons and, more preferably, about 1400 to about 1600 daltons. The R3 moieties range from 0 up to about 50% by weight of EO, preferably 0-40% EO. It is preferred that these moieties, when present, have a BAMW in the range of from about 300 to about 750 daltons.
There may also be more than one different polyether from each group. For example, a copolymer may comprise (a) two R1-type polyethers differing in molecular weight and/or EO-content, e.g., 55% EO of 4000 MW and 44% EO of 5500 MW, and (b) an R2-type polyether. In addition, butylene oxide can be substituted for propylene oxide in the polyether backbone. The polyether moieties can be linear or branched and can contain any number of carbon atoms.
The alkyl pendant groups, R4, can be C1-C12 substituted or unsubstituted alkyl groups, aryl groups, or alkaryl groups. Z is preferably xe2x80x94C(O)CH3 or CH3. B is preferably an allyl derivative, e.g., propyl, or a methallyl derivative, e.g., isobutyl.
These copolymer compositions possess an x/y ratio of less than or equal to about 10 for optimal FR performance. See U.S. Pat. No. 4,814,409.
Copolymer compositions having average target MWs with low to moderate values. e.g., less than about 21,000 daltons, are preferred. The average target MW is calculated as a simple sum of the building blocks comprising the silicone polyether block copolymer structure. Specifically, this value is a sum of the average silicone backbone MW and the product of the combined BAMW of pendant groups R1, R2, R3, and R1 with the average number of branch points per average chain. Molar excess amounts of pendant groups required for commercial syntheses of these copolymers or differential rates of addition of unique pendant compositions to the silicone backbone are ignored in the simple calculation of the average target MW.
As an example, the average target MW of a silicone surfactant comprised of a silicone backbone of 6,000 daltons MW on average with an average of 8 pendants per chain with a combined pendant BAMW of 2,000 daltons would be 22,000 daltons, i.e., 6,000+(8xc3x972,000).
Preparation of this type of copolymer is disclosed in U.S. Pat. Nos. 4,814,409 and 5,145,879, which are incorporated herein by reference.
The surfactants employed in the practice of the present invention are used in the preparation of foams that are blown using Dissolved Gas Technology. A given foam is usually comprised, at a minimum, of (a) a polyether polyol containing an average of more than two hydroxyl groups per molecule; (b) an organic polyisocyanate; (c) at least one catalyst for the production of polyurethane foams; (d) water; (e) a surfactant as defined above; and (f) an inert gas. All of these materials are known in the art, see U.S. Pat. Nos. 4,814,409 and 4,855,329, which are incorporated herein by reference.
The polyols have an average number of hydroxyl groups per molecule of at least slightly above 2 and, typically, from about 2.1 to about 3.5. The organic polyisocyanates contain at least two isocyanate groups, e.g., toluene diisocyanates (TDI), and the index of the foam is typically 60 to 130. The catalyst is usually an amine, such as triethylene diamine, bis(2-dimethylaminoethyl) ether, or mixtures thereof, and certain metal catalysts, including organic derivatives of tin, particularly tin compounds of octanoic acid or lauric acid. Other additives may be added to the polyurethane foam to impart specific properties to the foam, including, but not limited to, coloring agents, flame-retardants, and GEOLITE(copyright) Modifier foam additives (available from OSi Specialties, Inc. of Greenwich, Conn.).
The inert gas is one that is soluble in the foam formulation at elevated pressures, but will come out of solution, i.e., blow, at atmospheric pressure. An example of such a gas is CO2, but nitrogen, air, or other common gases, including hydrocarbon gases, such as methane and ethane, can also be used.
The surfactants should be of the type described above and should be present at from about 0.05 to about 5.0 wt. percent of the total reaction mixture, preferably from about 0.8 to about 2.0 wt. percent. This weight percentage only includes the block copolymer species and not the excess polyether and/or diluent or carrier of the surfactant. The diluent or carrier can be used for accurate metering purposes and/or surfactant viscosity reduction.
The foam is manufactured by mixing the ingredients together and putting them under high pressure, i.e., a pressure that is at least greater than atmospheric pressure, so that the inert gas is dissolved in the foaming mixture. Then, the mixture is subjected to controlled pressure reduction, which causes the gas to form bubbles at nucleation sites in the foaming system and thus act as a blowing agent. This produces a reduced density foam. For a more complete description of the process and the equipment required therein, see European Patent Publication No. 0 645 226 A2 or an equivalent thereof, e.g, U.S. Pat. No. 5,665,287; as well as U.S. Pat. No. 6,005,014; U.S. Pat. No. 6,147,133, and U.S. Pat. No. 6,326,413; which are all incorporated herein by reference.
The foam cell structure is typically uniform and fine and the bulk foam stability is good to excellent when Dissolved Gas Technology foams are prepared with the noted surfactant compositions, whereas, comparatively higher average target MW surfactant compositions and/or those with high EO content branches produce foams of coarser cell structure and/or reduced bulk foam stability. Fine cell structures are highly desired, with smaller cells, i.e., more cells per cm, in such foams being most desirable. Specifically, more than 7 cells per centimeter are normally desired and more than 14-16 cells per centimeter are preferred.
The polyurethane foams produced in accordance with the present invention can be used in the same fields as conventional polyether polyurethane foams. For example, the foams of the present invention can be used to advantage in the manufacture of textile interliners, cushions, mattresses, padding, carpet underlay, packaging, gaskets, sealers, thermal insulators, and the like.